Act as a MX backup

Background

In DNS it is possible to configure a domain to have multiple
mail exchange(MX) records. The different MX records have different
preferences or priority. The sender of an e-mail will first try to deliver
to the MX with the lowest preference, and then to the others.
The e-mail servers running on the MX records with high preference
can therefore be seen as backup mail servers.

Example

Host

Preference

mail.hmailserver.com

25

mail-backup.hmailserver.com

50

The sender of an email to me will first try to deliver to my server, mail.hmailserver.com. If the
delivery to my host fails for any reason, for example, due to network errors or
a machine crash, the sender will try to deliver to the server, mail-backup.hmailserver.com.
The server mail-backup.hmailserver.com will then have to forward the email to mail.hmailserver.com
whenever that goes online. The steps show how to configure the hMailServer
installation running on mail-backup.hmailserver.com to forward all email for the
domain hmailserver.com to the host mail.hmailserver.com.

Steps

Start up hMailAdmin.

Go to the Settings

Expand the SMTP settings node

Select Routes and click Add.

Specify the following:

Domain - The name of the domain you wish to backup. This should not be a domain configured on your server.

Target SMTP Host - The host name or, preferably, the IP address of the computer all e-mails to the domain should be forwarded to.

TCP Port - The TCP/IP port that the Target SMTP host is listening on.

Security - This option lets you specify on which IP range security should be
applied when someone tries to deliver to this route. Unless you have modified
the IP ranges, the default behaviour is: 1) A local domain - Anyone can send email
through your server to this domain. 2) An external domain - Only people who are
authenticated can send email through your server to this domain.

Address page - If you have a list of the existing e-mail addresses
on the target SMTP host, you can specify them here. If you do this, hMailServer
will reject e-mail sent to non-existing addresses.

Delivery page - Specify the number of times hMailServer should try
to deliver to this server.